The present invention relates to an aiming mechanism for a vehicular headlamp.
FIG. 12 and FIG. 13 illustrate a conventional aiming mechanism for a movable unit type vehicular headlamp. In the conventional aiming mechanism, a lamp body reflector unit 2, which has a light source mounted therein and is a tiltable member whose tilt angle defines the illumination angle of the headlamp beam, is supported at a point in the front of a lamp housing 1, which is a stationary member, by a tilting pivot (not shown) and by an aiming screw 3, which can move forward and backward in its axial direction. The lamp housing 1 is provided with a gear case 1a. In this gear case 1a, a nut member 4, which is threadedly joined with the aiming screw 3 extending to the front and penetrating forward and backward through the lamp housing 1, is supported in such a manner that the nut member 4 is enabled to rotate. At the front end portion of the aiming screw 3, a ball part 3a is formed and connected to a ball receiving part 2a, thus being prevented from rotating. Reference numeral 3b indicates an engaging part provided between the ball part 3a and the ball receiving part 2a for preventing the aiming screw from rotating.
Further, a bevel gear 5 is formed in a unified structure on the outer circumference of the nut member 4. A bevel gear 7, which meshes with the bevel gear 5, is provided on an operating shaft 6, which, being supported on the gear case 1a in such a manner as to be enabled to rotate, extends upward while crossing at right angles with the aiming screw 3. When the operating shaft 6 is rotated, the nut member 4 is rotated by way of the bevel gears 7 and 5. The aiming screw 3, which is prevented from rotating, thus moves forward or backward in the axial direction (i.e., in the direction indicated by an arrow), causing the ball receiving part 2a to move forward or backward, and hence tilting the lamp body reflector unit 2 around the pivot, whereby an adjustment is made of the aiming angle of the headlamp beam.
However, the conventional construction discussed above requires a pair of bevel gears 5 and 7 and a separate operating shaft 6. This presents a problem in that a large number of component parts are required, entailing a high cost.
Moreover, it is desirable for the aiming screw to move forward and backward in a smooth manner when the operating shaft 6 is rotated, for which purpose the operating shaft 6 and the nut member 4 must rotate smoothly. The sliding surfaces between the operating shaft 6 and the nut member 4 and the gear case 1a are made smooth so that the sliding friction therebetween is reduced to as small a value as possible. On the other hand, if smooth rotation is provided among the operating shaft 6, the nut member 4, and the aiming screw 3, there is a problem that the illumination angle of the headlamp tends eventually to come out of adjustment because vibration transmitted via the vehicle body can cause the nut member 4 and the operating shaft 6 to rotate, causing the aiming screw 3 to move forward or backward.